P-cscf discovery through nrf

ABSTRACT

A solution for establishing a data traffic session (e.g., a voice call or a video call) for a user equipment (UE) on a network (e.g., a 5G cellular network) comprises: receiving, by a session management node, from a network repository, identification of a first session control node and a second session control node; receiving, by the session management node, from the UE, a request for identifying a session control node for supporting the data traffic session; determining whether the first session control node is available; and based on at least determining that the first session control node is available and not determining that the second session control node is available, sending, by the session management node, to the UE, identification of the first session control node and not sending identification of the second session control node.

BACKGROUND

In order to make a voice or video call in 5G, a user device (UE, e.g.,cellphone or user equipment) sends a session initiation protocol (SIP)message to a proxy-call session control function (P-CSCF) node. The UEobtains a list of P-CSCFs from a session management function (SMF) node,randomly selects a P-CSCF from the list, and attempts to initiate thecall via the selected P-CSCF node. Upon a failure (e.g., the P-CSCF isunavailable), as may be determined by a time-out period with no responsefrom the P-CSCF (or a reject message), the UE will try another P-CSCF onthe list. The unavailability of the first P-CSCF contacted by the UEthus introduces a delay.

The SMF obtains identification of P-CSCFs from a DNS (domain namesystem) server, with updates at approximately 15 minute intervals. If aP-CSCF goes down shortly after an update, the SMF will be providing UEswith identification of the unavailable P-CSCF for a significant periodof time. Any UE that receives the stale P-CSCF information and selectsthe unavailable P-CSCF will experience an unnecessary delay, ofapproximately the length of the time-out period. This may degrade theuser's experience.

SUMMARY

The following summary is provided to illustrate examples disclosedherein, but is not meant to limit all examples to any particularconfiguration or sequence of operations.

A solution for establishing a data traffic session (e.g., a voice callor a video call) for a user equipment (UE) on a network (e.g., a 5Gcellular network) comprises: receiving, by a session management node,from a network repository, identification of a first session controlnode and a second session control node; receiving, by the sessionmanagement node, from the UE, a request for identifying a sessioncontrol node for supporting the data traffic session; determiningwhether the first session control node is available; and based on atleast determining that the first session control node is available andnot determining that the second session control node is available,sending, by the session management node, to the UE, identification ofthe first session control node and not sending identification of thesecond session control node.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed examples are described below with reference to theaccompanying drawing figures listed below, wherein:

FIG. 1 illustrates an exemplary arrangement that may advantageouslyestablish a data traffic session for a user equipment (UE) on a network,using proxy-call session control function (P-CSCF) discovery through anetwork resource function (NRF);

FIG. 2 illustrates a messaging sequence that may be used within thearrangement of FIG. 1;

FIG. 3 illustrates a flow chart of exemplary operations associated thearrangement of FIG. 1;

FIG. 4 illustrates another flow chart of exemplary operations associatedwith the arrangement of FIG. 1; and

FIG. 5 illustrates a block diagram of a computing device that may beused as a component of the arrangement illustrated in FIG. 1.

Corresponding reference characters indicate corresponding partsthroughout the drawings. References made throughout this disclosure.relating to specific examples, are provided for illustrative purposes,and are not meant to limit all implementations or to be interpreted asexcluding the existence of additional implementations that alsoincorporate the recited features.

DETAILED DESCRIPTION

A solution for establishing a data traffic session (e.g., a voice callor a video call) for a user equipment (UE) on a network (e.g., a 5Gcellular network) comprises: receiving, by a session management node(e.g., a session management function (SMF) node), from a networkrepository (e.g., a network repository function (NRF) node),identification of a first session control node and a second sessioncontrol node (e.g., a first and second proxy-call session controlfunction (P-CSCF) node); receiving, by the session management node, fromthe UE, a request for identifying a session control node for supportingthe data traffic session; determining whether the first session controlnode is available; and based on at least determining that the firstsession control node is available and not determining that the secondsession control node is available, sending, by the session managementnode, to the UE, identification of the first session control node andnot sending identification of the second session control node.

Aspects of the disclosure thus improve the speed of cellular voice andvideo call setup by, based on at least determining that the firstsession control node is available and that the third session controlnode is available, and not determining that the second session controlnode is available, sending, by the session management node, to the UE,identification of the first session control node and the third sessioncontrol node and not sending identification of the second sessioncontrol node. The SMF obtaining a list of available P-CSCFs from theNRF, rather than from a domain name system (DNS) server, improvesexpected call setup time. This is because the risk that a UE willexperience an unnecessary delay of approximately the length of a P-CSCFtime-out period is reduces.

A P-CSCF may register itself with the NRF, which functions to maintainup-to-date lists of available network resources, for example, a P-CSCFmay interface with the NRF using protocols similar to what a PolicyControl Function (PCF) uses to interface with the NRF. By usingheartbeat signals, the NRF is able to detect when a P-CSCF goes down.Upon a P-CSCF going down, the NRF may remove that P-CSCF from a listthat is sent to SMFs (upon an SMF discovery request) and may also pushout a notification to SMFs that a formerly-available P-CSCF is nowunavailable. The SMF is thus more timely updated about an unexpectedavailability of a P-CSCF and so will not identify the newly unavailableP-CSCF to a UE. The UEs will not have the newly unavailable P-CSCF onits list of P-CSCF candidates from which to select, thereby reducing therisk of a time-out.

FIG. 1 illustrates an exemplary arrangement 100 that may advantageouslyestablish a data traffic session 106 for a UE 102 on a network 110. Datatraffic sessions include voice and video calls between UE 102 and acalled device, such as a UE 104, over an Internet Protocol (IP)Multimedia SubSystem (IMS) core network. The call will pass from UE 102,over an air interface 114, through a radio access network (RAN) 112, auser plane function (UPF) 140, a selected one of a plurality of sessioncontrol nodes 144 a, 144 b, and 144 c (e.g., P-CSCF nodes), and an IMSAccess Media Gateway (IMS-AGW) 146. In some examples, each of sessioncontrol nodes 144 a, 144 b, and 144 c includes IMS Application LevelGateway (IMS-ALG) functionality. Although only a single UPF 140 and asingle IMS-AGW 146 are shown, it should be understood that network 110may have multiple ones of each type of node.

UE 102 learns the identification of session control nodes 144 a, 144 b,and/or 144 c from a session management node 120 (e.g., an SMF node),which has a list 132 of available ones of session control nodes 144 a,144 b, and 144 c. UE 102 communicates with a selected one of sessioncontrol nodes 144 a, 144 b, and 144 c using session initiation protocol(SIP) messages 150. UE 102 communicates with session management node 120via an access node 122 (e.g., an access and mobility management function(AMF) node). Session management node 120 obtains list 132 from a networkrepository 130 (e.g., an NRF node), rather than from a DNS server 126.In some examples, session management node 120 further updates list 132based on notifications received from network repository 130, for examplea notification that session control node 144 b has become unavailable.

Each of session control nodes 144 a, 144 b, and 144 c registers withnetwork repository 130, and network repository 130 may monitor (detect)the availability of session control nodes using heartbeat signals (timedby with a timer 136). When timer 136 lapses with a heartbeat signalmissing, network repository 130 may determine that the correspondingcontrol node is unavailable. This permits network repository 130 to havetimely status information regarding the availability of session controlnodes 144 a, 144 b, and 144 c. In some examples, session control nodes144 a, 144 b, and 144 c may use a protocol to communicate with networkrepository 130 that is similar to the protocol used by a policy controlfunction (PCF) node 124. PCF node 124 performs network slicing, roamingand mobility management, and supports quality of service (QoS) policyand charging control functions. List 132 is illustrated as containing asession control node identification 134 a for session control node 144a, a session control node identification 134 b for session control node144 b, and a session control node identification 134 c for sessioncontrol node 144 c. It should be understood that a different number ofsession control nodes may be identified in list 132.

Session control node identification 134 b is shown in a dashed box toindicate that after, list 132 was compiled by network repository 130(e.g., by each of session control nodes 144 a, 144 b, and 144 cregistering with network repository 130), session control nodeidentification 134 b is removed from list 132 at session management node120 and network repository 130. Network repository 130 removes sessioncontrol node identification 134 b from its copy of list 132 based on atleast the heartbeat signal from session control node 144 b ceasing.Network repository 130 also pushes a notification to session managementnode 120 that session control node 144 b is unavailable. Sessionmanagement node 120 removes session control node identification 134 bfrom its copy of list 132 based on at least receiving the notificationfrom network repository 130 that session control node 144 b isunavailable.

Further description of FIG. 1 will be made with additional reference toFIGS. 2 and 3. FIG. 2 is a messaging sequence diagram 200 that shows aseries of messages may be used within arrangement 100, and is describedin conjunction with FIG. 3. FIG. 3 illustrates a flow chart 300 ofexemplary operations associated with initiating data traffic session 106for UE 102 on network 110, and the messages of messaging sequencediagram 200 occur during various operations of flow chart 300. In someexamples, data traffic session 106 comprises a voice call or a videocall. In some examples, at least a portion of messaging sequence diagram200 and at least a portion of flow chart 300 may each be performed usingone or more computing devices 500 of FIG. 5. FIGS. 1-3 should be viewedtogether.

At 302 (see FIG. 3), each of session control nodes 144 a, 144 b, and 144c registering with network repository 130 using registration requestmessages 202 a, 202 b, and 202 c, respectively (see FIG. 2). Networkrepository 130 responds with resource created messages 204 a, 204 b, and204 c, respectively. Operation 302 thus includes detecting, by networkrepository 130, that session control node 144 a (a first session controlnode) is available, session control node 144 b (a second control node)is available, and session control node 144 c (a third session controlnode) is available. In some examples, network repository 130 comprisesan NRF node. In some examples, session control node 144 a, sessioncontrol node 144 b, and session control node 144 c each comprises aP-CSCF node. Network repository 130 places session control nodeidentification 134 a for session control node 144 a, session controlnode identification 134 b for session control node 144 b, and sessioncontrol node identification 134 c for session control node 144 c intolist 132. In operation 304, network repository 130 monitors availabilityof session control nodes 144 a, 144 b, and 144 c using a heartbeatsignal 206 a from session control node 144 a, a heartbeat signal 206 bfrom session control node 144 b, and heartbeat signal 206 c from sessioncontrol node 144 c.

At 306, session management node 120 sends a discovery message 208 tonetwork repository 130. Operation 306 thus includes receiving, bynetwork repository 130, from session management node 120, a request foridentifying available session control nodes. In some examples, sessionmanagement node 120 comprises an SMF node. Operation 308 includessending, by network repository 130, to session management node 120, theidentification of session control node 144 a, session control node 144b, and session control node 144 c in list 132, using a message 210.Operation 310 includes receiving, by session management node 120, fromnetwork repository 130, identification of session control node 144 a,session control node 144 b, and session control node 144 c. Operation312 includes storing, by session management node 120, list 132 ofsession control nodes 144 a, 144 b, and 144 c identified by networkrepository 130.

As indicated in FIG. 2, heartbeat signal 206 a from session control node144 a and heartbeat signal 206 c from session control node 144 ccontinue, but heartbeat signal 206 b from session control node 144 bceases. A decision operation 314 (in FIG. 3), also indicated as adetection 212 (in FIG. 2) includes detecting, by network repository 130,that session control node 144 b has become unavailable. Operation 316includes removing, by network repository 130, session control node 144 bfrom list 132 of session control nodes, for example, the copy of list132 maintained by network repository 130. That is, network repository130 removes session control node identification 134 b for sessioncontrol node 144 b from its copy of list 132. At 318, network repository130 notifies session management node 120 using a notification message214. Operation 318 includes pushing, by network repository 130, tosession management node 120, a notification that session control node144 b is unavailable. In some examples, session management node 120polls network repository 130 for list 132 on a repeating schedule.

Session management node 120 maintains its own copy of list 132, which isupdated in operation 320, also indicated as an update 216. Operation 320includes based on at least receiving the notification that sessioncontrol node 144 b is unavailable, removing session control node 144 bfrom list 132 of session control nodes, for example, the copy of list132 maintained by session management node 120. Session management node120 removes session control node identification 134 b for sessioncontrol node 144 b from its copy of list 132. Thus, each of operations316 and 317 include removing session control node 144 b from list 132 ofsession control nodes. Removal from the copy maintained by networkrepository 130 prevents session control node 144 b from being identifiedto any other session management nodes that send a discovery message tonetwork repository 130, requesting a list of available session controlnodes. Removal from the copy maintained by session management node 120prevents session control node 144 b from being identified to any UEsthat send a query message to session management node 120, requesting alist of available session control nodes.

UE 102 requests list 132, of available session control nodes, fromsession management node 120, in operation 322, using a query message218. Operation 322 also includes receiving, by session management node120, from UE 102, a request for identifying a session control node forsupporting data traffic session 106. In some examples, receiving therequest for identifying a session control node comprises receiving therequest for identifying a session control node through access node 122.In some examples, access node 122 comprises an AMF node. Operation 322may also be cast as include determining, by session management node 120,whether session control node 144 a is available. This may occur whendetermining that session control node 144 a is available compriseslocating session control node 144 a in list 132 of session control node.Operation 322 may also include determining, by session management node120, that session control node 144 c is available (e.g., if sessioncontrol node 144 c is located on list 132).

Operation 324 includes, based on at least determining that sessioncontrol node 144 a is available and not determining that session controlnode 144 b is available, sending, by session management node 120, to UE102, identification of session control node 144 a and not sendingidentification of session control node 144 b. In some examples,operation 324 includes, based on at least determining that sessioncontrol node 144 a is available and that session control node 144 c isavailable, and not determining that session control node 144 b isavailable, sending, by session management node 120, to UE 102,identification of session control node 144 a and session control node144 c and not sending identification of session control node 144 b. Thatis list 132 is sent with session control node identification 134 a forsession control node 144 a, and session control node identification 134c for session control node 144 c, but session control nodeidentification 134 b for session control node 144 b is not on list 132(Having been removed in operation 320). Operation 324 uses a message220.

Operation 326 includes receiving, by UE 102, the identification ofsession control node 144 a and session control node 144 c (in list 132).An operation 328, also indicated as a selection 222, includes, based onat least receiving, by UE 102, the identification of session controlnode 144 a and session control node 144 c, selecting, by UE 102, sessioncontrol node 144 a as a primary session control node from among sessioncontrol node 144 a and session control node 144 c. In some examples,this selection is performed randomly.

At 330, UE 102 sends a session initiation message 224 a (e.g., a SIPinvite), which is forwarded by UPF 140 to session control node 144 a asa message 224 b, which is further forwarded to IMS-AGW 146 as a message224 c (and then on to the called device, UE 104). Operation 332 includesreceiving, by session control node 144 a, from UE 102, a sessioninitiation message (224 a, 224 b) requesting data traffic session 106.In some examples, the session initiation message comprises a SIPmessage. In some examples, receiving the session initiation messagecomprises receiving the session initiation message through a UPF node.

Alternate configurations may be used, in some examples. Operation 334includes, based on at least receiving identification of session controlnode 144 a, establishing the data traffic session for UE 102 usingsession control node 144 a. This occurs when IMS-AGW 146, sessioncontrol node 144 a, and UPF 140 respond with acceptance messages 226 a,226 b, and 226 c, respectively. Messages 224 a-226 c are within SIPmessages 150 (shown in FIG. 1).

FIG. 4 illustrates a flow chart 400 of exemplary operations associatedwith establishing a data traffic session for a UE on a network. In someexamples, at least a portion of flow chart 400 may be performed usingone or more computing devices 500 of FIG. 5. Operation 402 includesreceiving, by a session management node, from a network repository,identification of a first session control node and a second sessioncontrol node. Operation 404 includes receiving, by the sessionmanagement node, from the UE, a request for identifying a sessioncontrol node for supporting the data traffic session. Operation 406includes determining whether the first session control node isavailable. Operation 408 includes based on at least determining that thefirst session control node is available and not determining that thesecond session control node is available, sending, by the sessionmanagement node, to the UE, identification of the first session controlnode and not sending identification of the second session control node.

FIG. 5 illustrates a block diagram of computing device 500 that may beused as a component of arrangement 100 of FIG. 1, for example, as anycomponent described herein that may require computational or storagecapacity. Computing device 500 has at least a processor 502 and a memory504 that holds program code 510, data area 520, and other logic andstorage 530. Memory 504 is any device allowing information, such ascomputer executable instructions and/or other data, to be stored andretrieved. For example, memory 504 may include one or more random accessmemory (RAM) modules, flash memory modules, hard disks, solid-statedisks, persistent memory devices, and/or optical disks. Program code 510comprises computer executable instructions and computer executablecomponents including any instructions necessary to perform operationsdescribed herein. Data area 520 holds any data necessary to performoperations described herein. Memory 504 also includes other logic andstorage 530 that performs or facilitates other functions disclosedherein or otherwise required of computing device 500. An input/output(I/O) component 540 facilitates receiving input from users and otherdevices and generating displays for users and outputs for other devices.A network interface 550 permits communication over a network 560 with aremote node 570, which may represent another implementation of computingdevice 500. For example, a remote node 570 may represent another of theabove-noted nodes within arrangement 100.

ADDITIONAL EXAMPLES

An exemplary system for establishing a data traffic session for a UE ona network comprises: a processor; and a computer-readable medium storinginstructions that are operative upon execution by the processor to:receive, by a session management node, from a network repository,identification of a first session control node and a second sessioncontrol node; receive, by the session management node, from the UE, arequest for identifying a session control node for supporting the datatraffic session; determine whether the first session control node isavailable; and based on at least determining that the first sessioncontrol node is available and not determining that the second sessioncontrol node is available, send, by the session management node, to theUE, identification of the first session control node and not sendidentification of the second session control node.

An exemplary method of establishing a data traffic session for a UE on anetwork comprises: receiving, by a session management node, from anetwork repository, identification of a first session control node and asecond session control node; receiving, by the session management node,from the UE, a request for identifying a session control node forsupporting the data traffic session; determining whether the firstsession control node is available; and based on at least determiningthat the first session control node is available and not determiningthat the second session control node is available, sending, by thesession management node, to the UE, identification of the first sessioncontrol node and not sending identification of the second sessioncontrol node.

One or more exemplary computer storage devices has computer-executableinstructions stored thereon for establishing a data traffic session fora UE on a network, which, on execution by a computer, cause the computerto perform operations comprising: receiving, by a session managementnode, from a network repository, identification of a first sessioncontrol node and a second session control node; receiving, by thesession management node, from the UE, a request for identifying asession control node for supporting the data traffic session;determining whether the first session control node is available; andbased on at least determining that the first session control node isavailable and not determining that the second session control node isavailable, sending, by the session management node, to the UE,identification of the first session control node and not sendingidentification of the second session control node.

Alternatively, or in addition to the other examples described herein,examples include any combination of the following:

-   -   based on at least receiving identification of the first session        control node, establishing the data traffic session for the UE        using the first session control node;    -   receiving, by the session management node, from the network        repository, identification of a third session control node;    -   based on at least receiving the request for identifying a        session control node, determining, by the session management        node, that the third session control node is available;    -   based on at least determining that the first session control        node is available and that the third session control node is        available, and not determining that the second session control        node is available, sending, by the session management node, to        the UE, identification of the first session control node and the        third session control node and not sending identification of the        second session control node;    -   detecting, by the network repository, that the first session        control node is available and that the second session control        node is available;    -   receiving, by the network repository, from the session        management node, a request for identifying available session        control nodes;    -   sending, by the network repository, to the session management        node, the identification of the first session control node and        the second session control node;    -   detecting, by the network repository, that the second session        control node has become unavailable;    -   pushing, by the network repository, to the session management        node, a notification that the second session control node is        unavailable;    -   storing, by the session management node, a list of session        control nodes identified by the network repository;    -   based on at least receiving the notification that the second        session control node is unavailable, removing the second session        control node from the list of session control nodes;    -   determining that the first session control node is available        comprises locating the first session control node in the list of        session control nodes;    -   the session management node comprises an SMF node;    -   the network repository comprises an NRF node;    -   the first session control node and the second session control        node each comprises a P-CSCF node;    -   the data traffic session comprises a voice call or a video call;    -   receiving, by the first session control node, from the UE, a        session initiation message requesting the data traffic session,        wherein the session initiation message comprises an SIP message;    -   receiving the session initiation message comprises receiving the        session initiation message through a UPF node;    -   receiving the request for identifying a session control node        comprises receiving the request for identifying a session        control node through an access node;    -   the access node comprises an AMF node;    -   the network repository monitors availability of session control        nodes using heartbeat signals;    -   based on at least receiving, by the UE, the identification of        the first session control node and the third session control        node, selecting, by the UE, the first session control node as a        primary session control node from among the first session        control node and the third session control node;    -   determining whether the first session control node is available        comprises determining, by the session management node, whether        the first session control node is available; and    -   removing the second session control node from the list of        session control nodes comprises removing, by the session        management node, the second session control node from the list        of session control nodes.

The order of execution or performance of the operations in examples ofthe disclosure illustrated and described herein is not essential, unlessotherwise specified. That is, the operations may be performed in anyorder, unless otherwise specified, and examples of the disclosure mayinclude additional or fewer operations than those disclosed herein. Forexample, it is contemplated that executing or performing a particularoperation before, contemporaneously with, or after another operation iswithin the scope of aspects of the disclosure. It will be understoodthat the benefits and advantages described above may relate to oneembodiment or may relate to several embodiments. When introducingelements of aspects of the disclosure or the examples thereof, thearticles “a,” “an,” “the,” and “said” are intended to mean that thereare one or more of the elements. The terms “comprising,” “including,”and “having” are intended to be inclusive and mean that there may beadditional elements other than the listed elements. The term “exemplary”is intended to mean “an example of.”

Having described aspects of the disclosure in detail, it will beapparent that modifications and variations are possible withoutdeparting from the scope of aspects of the disclosure as defined in theappended claims. As various changes may be made in the aboveconstructions, products, and methods without departing from the scope ofaspects of the disclosure, it is intended that all matter contained inthe above description and shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

1. A method of establishing a data traffic session for a user equipment(UE) on a network, the method comprising: receiving, by a sessionmanagement node, from a network repository, identification of a firstsession control node and a second session control node; receiving, bythe session management node, from the UE, a request for identifying asession control node for supporting the data traffic session;determining whether the first session control node is available; andbased on at least determining that the first session control node isavailable and not determining that the second session control node isavailable, sending, by the session management node, to the UE,identification of the first session control node and not sendingidentification of the second session control node.
 2. The method ofclaim 1, further comprising: based on at least receiving identificationof the first session control node, establishing the data traffic sessionfor the UE using the first session control node.
 3. The method of claim1, further comprising: receiving, by the session management node, fromthe network repository, identification of a third session control node;based on at least receiving the request for identifying a sessioncontrol node, determining, by the session management node, that thethird session control node is available; and based on at leastdetermining that the first session control node is available and thatthe third session control node is available, and not determining thatthe second session control node is available, sending, by the sessionmanagement node, to the UE, identification of the first session controlnode and the third session control node and not sending identificationof the second session control node.
 4. The method of claim 1, furthercomprising: detecting, by the network repository, that the first sessioncontrol node is available and that the second session control node isavailable; receiving, by the network repository, from the sessionmanagement node, a request for identifying available session controlnodes; sending, by the network repository, to the session managementnode, the identification of the first session control node and thesecond session control node; detecting, by the network repository, thatthe second session control node has become unavailable; and pushing, bythe network repository, to the session management node, a notificationthat the second session control node is unavailable.
 5. The method ofclaim 4, further comprising: storing, by the session management node, alist of session control nodes identified by the network repository; andbased on at least receiving the notification that the second sessioncontrol node is unavailable, removing the second session control nodefrom the list of session control nodes; and wherein determining that thefirst session control node is available comprises locating the firstsession control node in the list of session control nodes.
 6. The methodof claim 1, wherein the session management node comprises a sessionmanagement function (SMF) node; wherein the network repository comprisesa network repository function (NRF) node; wherein the first sessioncontrol node and the second session control node each comprises aproxy-call session control function (P-CSCF) node; and wherein the datatraffic session comprises a voice call or a video call.
 7. The method ofclaim 1, further comprising: receiving, by the first session controlnode, from the UE, a session initiation message requesting the datatraffic session, wherein the session initiation message comprises asession initiation protocol (SIP) message.
 8. A system for establishinga data traffic session for a user equipment (UE) on a network, thesystem comprising: a processor; and a non-transitory computer-readablemedium storing instructions that are operative upon execution by theprocessor to: receive, by a session management node, from a networkrepository, identification of a first session control node and a secondsession control node; receive, by the session management node, from theUE, a request for identifying a session control node for supporting thedata traffic session; determine whether the first session control nodeis available; and based on at least determining that the first sessioncontrol node is available and not determining that the second sessioncontrol node is available, send, by the session management node, to theUE, identification of the first session control node and not sendidentification of the second session control node.
 9. The system ofclaim 8, wherein the operations are further operative to: based on atleast receiving identification of the first session control node,establish the data traffic session for the UE using the first sessioncontrol node.
 10. The system of claim 8, wherein the operations arefurther operative to: receive, by the session management node, from thenetwork repository, identification of a third session control node;based on at least receiving the request for identify a session controlnode, determining, by the session management node, that the thirdsession control node is available; and based on at least determiningthat the first session control node is available and that the thirdsession control node is available, and not determining that the secondsession control node is available, send, by the session management node,to the UE, identification of the first session control node and thethird session control node and not send identification of the secondsession control node.
 11. The system of claim 8, wherein the operationsare further operative to: detect, by the network repository, that thefirst session control node is available and that the second sessioncontrol node is available; receive, by the network repository, from thesession management node, a request for identifying available sessioncontrol nodes; send, by the network repository, to the sessionmanagement node, the identification of the first session control nodeand the second session control node; detect, by the network repository,that the second session control node has become unavailable; and push,by the network repository, to the session management node, anotification that the second session control node is unavailable. 12.The system of claim 11, wherein the operations are further operative to:store, by the session management node, a list of session control nodesidentified by the network repository; and based on at least receivingthe notification that the second session control node is unavailable,remove the second session control node from the list of session controlnodes; and wherein determining that the first session control node isavailable comprises locating the first session control node in the listof session control nodes.
 13. The system of claim 8, wherein the sessionmanagement node comprises a session management function (SMF) node;wherein the network repository comprises a network repository function(NRF) node; wherein the first session control node and the secondsession control node each comprises a proxy-call session controlfunction (P-CSCF) node; and wherein the data traffic session comprises avoice call or a video call.
 14. The system of claim 8, wherein theoperations are further operative to: receive, by the first sessioncontrol node, from the UE, a session initiation message requesting thedata traffic session, wherein the session initiation message comprises asession initiation protocol (SIP) message.
 15. One or more computerstorage devices having computer-executable instructions stored thereonfor establishing a data traffic session for a user equipment (UE) on anetwork, which, on execution by a computer, cause the computer toperform operations comprising: receiving, by a session management node,from a network repository, identification of a first session controlnode and a second session control node; receiving, by the sessionmanagement node, from the UE, a request for identifying a sessioncontrol node for supporting the data traffic session; determiningwhether the first session control node is available; and based on atleast determining that the first session control node is available andnot determining that the second session control node is available,sending, by the session management node, to the UE, identification ofthe first session control node and not sending identification of thesecond session control node.
 16. The one or more computer storagedevices of claim 15, wherein the operations further comprise: based onat least receiving identification of the first session control node,establishing the data traffic session for the UE using the first sessioncontrol node.
 17. The one or more computer storage devices of claim 15,wherein the operations further comprise: receiving, by the sessionmanagement node, from the network repository, identification of a thirdsession control node; based on at least receiving the request foridentifying a session control node, determining, by the sessionmanagement node, that the third session control node is available; andbased on at least determining that the first session control node isavailable and that the third session control node is available, and notdetermining that the second session control node is available, sending,by the session management node, to the UE, identification of the firstsession control node and the third session control node and not sendingidentification of the second session control node.
 18. The one or morecomputer storage devices of claim 15, wherein the operations furthercomprise: detecting, by the network repository, that the first sessioncontrol node is available and that the second session control node isavailable; receiving, by the network repository, from the sessionmanagement node, a request for identifying available session controlnodes; sending, by the network repository, from the session managementnode, the identification of the first session control node and thesecond session control node; detecting, by the network repository, thatthe second session control node has become unavailable; and pushing, bythe network repository, to the session management node, a notificationthat the second session control node is unavailable.
 19. The one or morecomputer storage devices of claim 18, wherein the operations furthercomprise: storing, by the session management node, a list of sessioncontrol nodes identified by the network repository; and based on atleast receiving the notification that the second session control node isunavailable, removing the second session control node from the list ofsession control nodes; and wherein determining that the first sessioncontrol node is available comprises locating the first session controlnode in the list of session control nodes.
 20. The one or more computerstorage devices of claim 15, wherein the session management nodecomprises a session management function (SMF) node; wherein the networkrepository comprises a network repository function (NRF) node; whereinthe first session control node and the second session control node eachcomprises a proxy-call session control function (P-CSCF) node; andwherein the data traffic session comprises a voice call or a video call.